There's a real time map of VHF propagation that uses APRS stations to automate the process. "The map is created using positions (latitude and longitude) reported by nodes in the packet radio system and the hops from node to node that the data travels. By correlating the hops with the position of each end of the hop, the distance can be inferred."

Edit: Title says VHF / UHF... the details of the page say that it's 2M APRS, but the guy in the club that wrote the piece for the newsletter worked stations well into VHF according to the article. I assume conditions favorable for VHF extend into UHF if everything is just right.